I love to watch them every year. Sometimes, their nest is easy to see and I watch the progress when I walk there in the morning. Other years, their nest is hidden, away from my path and my first inkling of a new spring is when I see the cygnets swimming along with their proud parents.
Below is some video I took on the same day. The background noise is the wind blowing.
For the most part swans mate for life but they will chose a new partner if one of the pair dies. Both parents will build the nest and both parents will sit on the eggs. They can also be fairly aggressive if they see you as a threat. I'm glad to have them close to the boardwalk this year, but not too close.
For some interesting information about Mute Swans from Cornell University click here.